The present invention relates generally to the field of subterranean exploration and drilling and, more particularly, to a method and system for accessing a subterranean zone from a limited surface area.
Subterranean deposits of coal, whether of xe2x80x9chardxe2x80x9d coal such as anthracite or xe2x80x9csoftxe2x80x9d coal such as lignite or bituminous coal, contain substantial quantities of entrained methane gas. Limited production and use of methane gas from coal deposits has occurred for many years. Substantial obstacles have frustrated more extensive development and use of methane gas deposits in coal seams. The foremost problem in producing methane gas from coal seams is that while coal seams may extend over large areas, up to several thousand acres, the coal seams are fairly shallow in depth, varying from a few inches to several meters. Thus, while the coal seams are often relatively near the surface, vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius around the coal deposits. Further, coal deposits are not amenable to pressure fracturing and other methods often used for increasing methane gas production from rock formations. As a result, once the gas easily drained from a vertical well bore in a coal seam is produced, further production is limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.
Prior systems and methods generally require a fairly level surface area from which to work. As a result, prior systems and methods generally cannot be used in Appalachia or other hilly terrains. For example, in some areas the largest area of flat land may be a wide roadway. Thus, less effective methods must be used, leading to production delays that add to the expense associated with degasifying a coal seam. Additionally, prior systems and methods generally require fairly large working surface area. Thus, many subterranean resources are inaccessible because of current mining techniques and the geographic limitations surrounding the resource. Additionally, potential disruption or devastation to the environment surrounding the subterranean resources often prevents the mining of many subterranean resources.
The present invention provides a method and system for accessing subterranean deposits from a limited surface area that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods.
In accordance with one embodiment of the present invention, a system for accessing a subsurface formation from a limited surface area includes a first well bore extending from the surface to a target zone. The first well bore includes an angled portion disposed between the target zone and the surface. The system also includes a second well bore extending from the surface to the target zone. The second well bore is offset from the first well bore at the surface and intersects the first well bore at a junction proximate the target zone. The system further includes a well bore pattern extending from the junction into the target zone.
In accordance with another embodiment of the present invention, a method for accessing a subsurface formation from a limited surface area includes forming a first well bore extending from the surface to a target zone. The first well bore includes an angled portion disposed between the target zone and the surface. The method also includes forming a second well bore extending from the surface to the target zone. The second well bore is offset from the first well bore at the surface and intersects the first well bore at a junction proximate the target zone. The method further includes forming a well bore pattern extending from the junction into the target zone.
Technical advantages of the present invention include providing an improved method and system for accessing subterranean deposits from a limited area on the surface. In particular, a well bore pattern is drilled in a target zone from an articulated surface well at least in close proximity to another or second surface well. The second surface well includes an angled portion to accommodate location of the second surface well in close proximity to the articulated well while providing an adequate distance at the target zone between the second surface well and the articulated well to accommodate the radius of the articulated well. The well bore pattern is interconnected to the second surface well through which entrained water, hydrocarbons, and other fluids drained from the target zone can be efficiently removed and/or produced. The well bore pattern may also be used to inject or introduce a fluid or substance into the subterranean formation. As a result; gas, oil, and other fluids from a large, low pressure or low porosity formation can be efficiently produced at a limited area on the surface. Thus, gas may be recovered from formations underlying rough topology. In addition, environmental impact is minimized as the area to be cleared and used is minimized.
Yet another technical advantage of the present invention includes providing an improved method and system for preparing a coal seam or other subterranean deposit for mining and for collecting gas from the seam after mining operations. In particular, a surface well, with a vertical portion, an articulated portion, and a cavity, is used to degasify a coal seam prior to mining operations. This reduces both needed surface area and underground equipment and activities. This also reduces the time needed to degasify the seam, which minimizes shutdowns due to high gas content. In addition, water and additives may be pumped into the degasified coal seam through the combined well prior to mining operations to minimize dust and other hazardous conditions, to improve efficiency of the mining process, and to improve the quality of the coal product. After mining, the combined well is used to collect gob gas. As a result, costs associated with the collection of gob gas are minimized to facilitate or make feasible the collection of gob gas from previously mined seams.